Ultra-low-cost coolant heating apparatus for electric vehicle applications

ABSTRACT

An ultra low cost electric vehicle heating apparatus, components thereof, and related method are herein described. A driver circuit operates a switching device at an intermediate state between fully-turned-off and fully-turned-on, in a high power dissipation heating mode, to efficiently produce heat energy for heating a passenger compartment, or energy storage system, of an electric vehicle. The driver circuit operates the switching device to have a fully-turned-off state and a fully-turned-on state in a main function mode for a traction inverter or an energy storage system charger of the electric vehicle. The driver circuit is operable to cycle the heating mode and the main function mode for combining such heating and such main function operation of the traction inverter, or the charger, without compromising the operation of the traction motor, or charger, while simultaneously eliminating many of the expensive resistive heating components in use by practitioners of the art.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit of priority from U.S. ProvisionalApplication No. 63/308,911 which is hereby incorporated by reference.

TECHNICAL FIELD

The technical field of the present disclosure relates generally toelectrically propelled vehicles (“EV”), more specifically heating ofelectrically propelled vehicles, and operation of traction inverters andonboard chargers, and drivers for traction inverters and onboardchargers.

BACKGROUND

Electric vehicles have many variations of powertrains, which typicallyfeature an energy storage system such as a battery or fuel cell,traction inverters or traction motor controllers, and electric motors,along with an onboard or offboard vehicle charging system. The variouscomponents of electric vehicles, their support equipment, and thepassengers thereof, have various heating and cooling needs that areaddressed with various technological solutions, some of which arereviewed herein. There is an ongoing need for improvements in electricvehicle technology and reduction in cost of electric vehicles. It is inthis context that present embodiments arise.

SUMMARY

Various embodiments of an electric vehicle heating system, tractioninverters, onboard chargers, driver circuits, and method of operationare described herein. Embodiments make use of a novel intermediatestate, between fully-turned-off and fully-turned-on, for operating aswitching device to intentionally produce high levels of Joule heatingin order to eliminate costly resistive heating components.

One embodiment is an electric vehicle (EV) heating system. The EVheating system includes at least a driver circuit, and may also includea controller, a traction inverter, an onboard charger, and/or componentsdefining a fluid path for heat exchange. The driver circuit is tooperate a switching device at an intermediate state betweenfully-turned-off and fully-turned-on, in a heating mode to produce highlevels of Joule heating for such intended purposes as heating apassenger compartment or the energy storage system of an electricallypropelled, or braked, vehicle while eliminating separate resistiveheating devices and their supporting components and systems to reducecost and weight. The driver circuit is to operate the switching deviceto have a fully-turned-off state and a fully-turned-on state in a mainfunction mode for a traction inverter or an onboard charger of theelectric vehicle. The driver circuit is operable to cycle the heatingmode and the main function mode for combining such heating and such mainfunction operation of the traction inverter or the onboard charger.

One embodiment is an electric vehicle heating system. The EV heatingsystem includes a traction inverter that has switching devices foroperating an electric motor, and driver circuits each coupled to one ormore of the switching devices. Each driver circuit is to operate theswitching device, or a plurality of switching devices, at anintermediate state between fully-turned-off and fully-turned-on, in aheating mode to produce high levels of Joule heating for such purposesas heating a passenger compartment or an energy storage system. Eachdriver circuit is to operate the switching device or a plurality ofswitching devices, to have a fully-turned-off state and afully-turned-on state in a main function mode for the traction inverter.Each driver circuit is to cycle the heating mode and the main functionmode for combined such heating and such main function operation of thetraction inverter.

One embodiment is a method of heating an electric vehicle. The methodincludes operating each of multiple switching devices of a tractioninverter through a respective driver circuit, to operate an electricmotor. The method includes operating at least one of the switchingdevices of the traction inverter through the driver circuit with theswitching device at an intermediate state between fully-turned-off andfully-turned-on, in a heating mode to produce high levels of Jouleheating. The method includes directing the Joule heating produced in theheating mode to heat at least a passenger compartment or an energystorage system.

Other aspects and advantages of the embodiments will become apparentfrom the following detailed description taken in conjunction with theaccompanying drawings which illustrate, by way of example, theprinciples of the described embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

The described embodiments and the advantages thereof may best beunderstood by reference to the following description taken inconjunction with the accompanying drawings. These drawings in no waylimit any changes in form and detail that may be made to the describedembodiments by one skilled in the art without departing from the spiritand scope of the described embodiments.

FIG. 1 depicts a hybrid/electric vehicle battery cooling system.

FIG. 2 depicts a hybrid/electric electronics system.

FIG. 3 depicts a hybrid/electric vehicle heater-coolant heater.

FIG. 4 depicts heating loops in an electric vehicle.

FIG. 5 depicts an example three-phase traction inverter for an electricmotor of an electric vehicle in accordance with some embodiments.

FIG. 6 illustrates a Table having space vector modulation strengths inaccordance with some embodiments.

FIG. 7 depicts an example isolated MOSFET drive circuit in accordancewith some embodiments.

FIG. 8 depicts example MOSFET characteristic curves in accordance withsome embodiments.

FIG. 9 depicts an embodiment of a drive circuit for an electric vehicleheating system in accordance with some embodiments.

FIG. 10 depicts an embodiment of an electric vehicle heating system thatuses the drive circuit of FIG. 9 or variation thereof.

FIG. 11 is a flow diagram of a method for an electric vehicle heatingsystem in accordance with some embodiments.

DETAILED DESCRIPTION

Described herein, in various embodiments, is a heating system forelectric vehicles, which can be implemented as an ultra-low cost energystorage system preheater and/or heater and/or occupant heater. Theembodiments create a novel electric vehicle traction inverter designthat adds a third mode of operation to high power output stage switchingdevices. Present state of the art has two fundamental states for outputstage switching of switching devices in high efficiency tractioninverters, irrespective of the number of levels of voltage outputproduced by the inverter architecture—a high conductivity, lowresistance, lowest power dissipation, fully-on switching state; and azero conductivity, infinite resistance, zero power dissipation fully-offswitching state. The present embodiments introduce a third switchingstate for a switching device, produced by a driver circuit that controlsthe switching device—a high power dissipation, semi-off, partiallyconductive, intermediate state (i.e., a state between fully-on state andfully-off state) which is selectively enabled in place of the zero powerdissipation fully-off state, enabling switching device(s) to be used asa useful, controllable, heat energy source for such purposes thatinclude vehicle cabin heating and energy storage systemheating/preconditioning to replace or augment resistive heating devicesand maximize overall vehicle efficiency by avoiding the dumping of heatfrom the traction inverter, or vehicle charger, overboard into theatmosphere and by eliminating the need to use, or reducing the amountof, power to utilize a heat pump device to move the heat from thetraction inverter, or vehicle charger, to another location. Thissemi-off, intermediate state operates in one embodiment as MOSFET(s)gate(s) driven slightly above threshold voltage, a typicallyuncharacterized power device operating region, creating a partiallyconductive channel that restricts, but has non-zero, current flow withhigh voltage applied across drain and source of the MOSFET, producingcontrollable, and high levels, of Joule heating that heats a coolantintended to transfer heat away from the MOSFET. It should be appreciatedthat heat can also be moved using conduction or convection instead of byfluids or phase change cooling/heating in some embodiments.

The present embodiments eliminate costly dedicated resistor-basedheating components, as found in electric vehicles for example, that areused as heat sources for thermal conditioning of vehicle components thatinclude such components as traction energy storage systems, and assources of heat energy for heating spaces and compartments, such as thevehicle cabin. While high power electronics are meticulously designedfor maximum efficiency, and heat energy losses are considereddetrimental, the present embodiment intentionally and selectivelyoperates such devices in such modes so as to act as electrical resistorsor current limiters/“throttles” to intentionally dissipate high levelsof power in the switching device in order to provide a source of highthermal power that is then transported to heat exchangers by such meansas conduction, convection, or by a liquid, phase change, or gas(including air) coolant to the device or environment in which thetemperature is to be raised. Such high current devices associated withan electric vehicle include switching devices (e.g., semiconductor-basedswitches) that control traction motors, that perform DC-DC conversion,that perform AC to DC charging, and that drive high powered motors thatinclude such devices as power steering pumps and air conditioningcompressors and pumps. Such devices may be located on or in the vehicleor may be associated with an electric vehicle from time to time such asa vehicle charging station. As such, the sources of heat are not bynecessity centralized and can produce heat for isolated coolant regimes,and may be transferred by such means as heat exchangers, or thermalmedia transfer, from one regime to another, as is currently practiced inthe art for electric vehicle thermal conditioning. One aspect of theembodiment is that it allows continuous control of the amount of heatthat is produced in one embodiment, whereas another method turns a highloss mode of operation on and off. It should be appreciated that thesemechanisms facilitate control of the temperature of the system in whichthe devices are thermally incorporated and provide a mechanism toexploit, minimize, and eliminate, waste heat that would otherwise bedumped overboard into the environment due to excessive power levelgeneration for a vehicle subsystem. The heat from the devices can bemoved from the lossy switching device source by means of conduction, aswould be exemplified by generating power in an air conditioning heatpump or compressor motor's semiconductor drivers in operation fortransporting heat from one location to another, or drying air ordefrosting a windshield, for example, by fluid (gas or liquid)transport, or by phase change or other suitable heat transfer/transportmechanisms. While high power devices, in the kilowatts regime of powercontrol are identified, nothing prevents scavenging of heat from lowerpower switching devices operating in an embodiment that uses the thirdswitching state, as well by such things as a heat pump or heat pipe,aggregating sources of heat. In one embodiment, the power devices areMOSFETS, which are typically run in a low resistance mode (high gatevoltage, low (R_(ds))-drain to source resistance, fully-on state) toproduce minimal waste heat and in a very high resistance mode (low oreven negative gate voltage, below threshold voltage, high drain tosource resistance, fully-off state). Such power switching devices areherein run in the “triode” or linear resistor region, or with a low gatevoltage and high drain to source voltage in the saturation region aspartially conductive current limiters by pinching off part of theconduction channel to produce an effective current throttle in theirconduction channels between the device source and drain terminals,creating a temperature rise because of the I²R, or V*I, power losses todeliberately produce Joule heating, which is a product of the square ofthe current through the power device and the resistance of theaforementioned conduction channel or simply the power dissipated bylimiting its current as a product of the applied voltage to it, V*I.Such modes of operation of a switching device in an intermediate statebetween fully-off and fully-on are novel in a traction inverter, andhave been completely oblivious to designers that strive for maximumsystem efficiency through use of switching devices only in the fully-onand fully-off states as operation in this third regime would be deemedinefficient. Datasheets from manufacturers of the high-power switchingdevices do not characterize or specify this near-threshold-voltageregion of device operation because it is simply not used by anyonepracticed in the art. Generally, this paradigm of striving forefficiency in a traction inverter is viewed from within the designer's“siloed” system design, which focuses only on the traction inverteritself. When the overall vehicle is considered, however, heat in theembodiments discussed herein is reused for productive purposes likeheating the passenger cabin or in heating the energy storage system formore efficient or higher energy delivery or acceptance. In that case,the heat intentionally generated by the instant embodiment is applied toproductive means, making the “wall plug efficiency” of the mobilitysolution more efficient by utilizing the heat that would have beendumped out of a radiator as a waste product of the switching process bypractitioners of the art taking pride in achieving “97% efficiency”, forexample, for their traction inverter subsystem which has its owndedicated cooling loop that dumps that 3% energy loss as heat overboardinto the environment. These high power switching devices are generallyliquid cooled to achieve million hour lifetimes, despite “the doorsfalling off the vehicle” after about 10,000 hours, i.e., projected lifespan of the power devices in an inverter is excessively longer thanprojected life span of many critical vehicle components and can beoperated at elevated temperatures without harming vehicle lifetime,particularly in one of the embodiments as a Silicon Carbide switchingdevice. As such, operating the switching devices at elevatedtemperatures in a third heating mode of switching does not affectoverall vehicle life or reliability as long as temperature limitationsare not exceeded.

Electric vehicles are used as a target application of one embodiment,though various embodiments could be used for other systems such aschemical processing plants, solar power systems, etc., varying somewhatin their schemes to thermally manage heat in the vehicle or othersystem. Some electric vehicles, for example the Chevrolet Bolt EV,partition their implementation into “islands” where each system isindependent of the other, while the most recent incarnations of theTesla Model 3/Y and Model S Plaid intermix everything and move the heataway from where it is undesirable to places is it needed though the useof a heat pump. The latter has proven itself not to be without flaws,with significant numbers of complaints from customers regarding aninability to heat the occupant cabin in extremely cold winterconditions, a well known limitation of heat pump systems where inhousehold applications, electric heating strips are provided as backupheat sources in rooms. While heat pumps can improve vehicle efficacythrough scavenging, to accommodate heating in winter conditions, thevehicle still requires a substantially sized supplemental heat source.

A review of the Chevrolet Bolt EV is presented first, then the presentreview progresses to the classical Tesla Model S cabin and batteryheating system, to show representative implementations by practitionersof the art. Since the present embodiment concerns itself with heating,focus of these reviews will be on heating and not on cooling of thevehicle systems or using heat pumps to move heat from one environment orcomponent/system to another. Again, these sources and scavenging methodsare not exclusive to electric mobility devices.

The Bolt EV has three independent thermal conditioning loops, somewhatmisleadingly called “cooling” by Chevrolet when they are in fact,“thermal management.” They are: 1) Hybrid/Electric Vehicle Battery‘Cooling’ System (FIG. 1), 2) Hybrid/Electric Electronics ‘Cooling’System (FIG. 2), and 3) Hybrid/Electric Vehicle Heater-coolant Heater(FIG. 3).

The Bolt EV heating/cooling loop, “Hybrid/Electric Vehicle Battery‘Cooling’ System”, shown in FIG. 1 is used to heat or cool the HighVoltage Traction Battery 1. Thermal energy is transferred to or from thebattery by means of a cooling plate 2. A coolant, typically ethyleneglycol or propylene glycol, is used to move thermal energy in a loop, inthis case the thermal energy from the battery cooling plate 2 to areservoir, or “surge tank” 3. The surge tank then gravity feeds avariable speed pump (4) that pumps coolant in a steady flow around theloop at varying flow rates depending on the amount of energy to bemoved. A general rule for lithium-based EV batteries is that they arepreferentially kept at “comfortable human” temperatures, in the case ofthe Bolt EV, above 65 degrees Fahrenheit. If the battery temperaturedrops below this threshold, it becomes less efficient at deliveringstored energy, and can be damaged if charged in excessively coldtemperatures, so it needs to be heated in cold weather. The pump 4circulates coolant through an electric heater 5, in the Bolt EV beingpowered from the ˜400 VDC battery by a control circuit, and providingapproximately 2 kW of thermal power to heat the coolant if the batterytemperature is below its threshold of operation. As an aside, in somevehicles, not the Bolt EV, the battery is heated to higher temperaturesprior to charging, on the order of 130° F.-140° F., to reduce theinternal resistance of the battery to enable high “fast charging”rates—this process of preheating the battery before charging is called“preconditioning” in those vehicles. The heated or non-heated coolantthen is routed to a heat exchanger (“HEX”) 6 where the coolant can haveits heat exchanged with the air conditioning refrigerant loop 7—in theBolt EV this HEX is used for cooling the non-heated coolant only. Fromthe HEX 6, the coolant is routed to the cooling plate 2 which transfersheat to/from the coolant, from/to the HV traction battery, by means ofthermal conduction.

The Bolt EV cooling loop, “Hybrid/Electric Electronics ‘Cooling’System”, shown in FIG. 2, is used to cool the vehicle's high powerelectronics. The “single power inverter module”, or SPIM 9, contains thehigh power drive electronics used to convert the ˜400 VDC high voltagetraction battery into a three phase alternating current of varyingfrequency, voltage, and current by methods known to those practiced inthe art. The SPIM is designed to be maximally efficient, with muchdesign effort to reduce the amount of waste heat produced in the processof “inverting” DC to AC for the traction motor. This loop only hasprovisions for cooling its components to ambient temperature viaradiator 16. In the Bolt EV, the traction motor is on the order of 150kW in power, and one can assume that the inverter normally operates withefficiency greater than 95%. At maximum power output, this means theinverter must dissipate up to 7.5 kW of heat, the equivalent of about ahalf dozen home space heaters. Fortunately, normal operation of thevehicle does not occur at maximum power levels for extended periods andactual “normal” driving uses about 18 kW to 30 kW of traction power fromthe motor, meaning about 900 W to 1.5 kW is to be dissipated as heat bythe SPIM. The liquid coolant is then routed from the SPIM 9, to the“Accessory Power Module” 10, or APM, which DC-DC converts the ˜400 VDCHV traction battery voltage to ˜12 VDC to be used by 12V vehicleaccessories and electronics and is used to charge an onboard 12V batteryto provide power to the vehicle electronics and accessories while the HVbattery is either disconnected or not in use. The APM replaces thealternator as found in an internal combustion vehicle, and delivers onthe order of 100 Amps of current at a nominal 12V or about 1200 W.Assuming 90% efficiency, this means at maximum power delivery, the APMwill need to dissipate approximately 120 W of power into the coolant.The higher power SPIM 9, precedes the APM 10. The coolant then splits totwo paths with a simply Y-connected pair of hoses, with one path being areturn to the top of the reservoir, or “Surge Tank” 11. The other halfof the coolant flow split goes to the onboard charger, OBC 12, whichonly operates when the vehicle is charging. The Bolt EV is capable ofcharging at 12 amps at 240 VAC, which is about 3 kW. Assuming 90%efficiency, this means about 300 W of power needs to be dissipated intothe coolant. The coolant then routes to a heat exchanger on the driveunit, HEX 13 to indirectly cool the oil used in the drive unit tolubricate moving parts and to extract heat from the motor components 14.The coolant then returns to the surge tank 11. From the surge tank, thecoolant is gravity fed to a variable speed motorized pump which impartsflow to the coolant to push it to the radiator 16, which is a liquid toair heat exchanger. The radiator's cooling efficacy is assisted by thevehicle airstream when motorized shutters are opened, as well as avariable speed fan 17. The cooled coolant then is routed to the SPIM 11to complete the loop.

The Bolt EV heating loop, “Hybrid/Electric Vehicle Heater-coolantHeater”, shown in FIG. 3 is used to heat the passenger cabin by heatingcoolant, then using a heater core to exchange that coolant heat with thecabin air. The coolant reservoir, or “Surge Tank” 22, is used to hold areserve of coolant. From the reservoir, coolant is gravity fed to avariable speed motorized pump 23, which then causes coolant to flow toan electric heater 24. This electric immersion heater 24 heats aresistive material using the HV traction battery's 400 VDC power, withon the order of a maximum of 7 kW of power, as delivered by the powerand control circuits 25. Nominally, this heater has been observed to useapproximately 2 kW to 3 kW in normal operation and the objective of theheater is to heat the coolant to a nominal 130 degrees Fahrenheit. Theheated coolant is then routed from the electric coolant heater 24 to awater to air heat exchanger 19, also known in the industry as a “heatercore”, housed in the passenger cabin 20. The heat transfer to the cabinair is maximized as needed by a variable speed motorized fan 21.

The Tesla Model S bears similarities to Bolt EV's loops. The Tesla'sheating loops are shown in FIG. 4. As in the Bolt EV FIGS. 1, 2 and 3,respectively, the Tesla divides cooling loops into three similardomains, each with a dedicated coolant pump, with similar affectedcomponents, namely battery heating/cooling 42, vehicle electronicscooling 26, and cabin heating and cooling 39. The Tesla, however,enables crossing over between coolant domains, where heated coolant fromthe vehicle electronics can be used to heat the cabin, facilitated byvalves 34, 35, 37 and can even use that heat to warm the battery via theheat exchanger HEX 46. An air conditioning system can be used to coolthe battery via HEX 46. Notably an electric immersion heater 44 is usedto warm coolant to heat the battery 45 and another electric heater 41 isused to warm the cabin air. In normal driving conditions, there simplyis not enough heat generated in the inverter 30 or the drive motor 31 toheat the cabin or to preheat a stationary car's battery in preparationfor charging. Newer generation Tesla vehicles use a heat pump toscavenge heat where possible, but in extremely cold weather, there isn'tenough heat being generated in the vehicle, or is present in coldambient air, to scavenge. The components in the vehicle were designed tominimize heat lost in their operation, which necessitates the inclusionof expensive heating element-equipped components in electric vehicles,as can be seen in FIG. 4 for cabin heating with significant additionalcost for battery heating modules and controllers. These electric heatersare also generally necessitated in heat pump equipped vehicles operatingin extremely cold weather conditions.

The embodiments described herein provide for a mechanism to reduce costand complexity of the overall system and recognize that electricallyproduced heat is drawn from the energy storage system (in an EV, an HV(high voltage) battery, for example) irrespective of the element thatgenerates that heat. Any “non-useful” heat dumped overboard via theradiator to the atmosphere is energy lost from the energy storage systemthat did not perform useful work or warming. Practitioners in the artare conditioned to maximize efficiency and reduce the heat produced byfunctional elements such as motor drive inverters and vehicle chargers,for example, and to throw that “minimized” heat away. To create the heatneeded by vehicle cabin occupants in cold weather, to heat the energystorage system to operate at its maximum efficacy in cold weather, andto enable the energy storage system to be replenished or depleted atvery high rates of charge or discharge, vehicle designers and architectsadd resistor-based electric heating devices in coolant loops associatedwith vehicle cabins and energy storage systems. The embodimentsdescribed herein dispose of these expensive resistor-based heatingdevices completely as needless devices, and intentionally repurpose andreuse existing components in the traction inverter described herein todeliberately generate Joule heating, in one traction inverter embodimentdiscussed here, in the vehicle charger in another embodiment, and inother embodiments can be applied to moderate to high power electronicsdriving such high loads of power steering, and air conditioning, pumpswhere heat is being scavenged by the likes of a heat pump or heat pipe.

In one embodiment MOSFET devices drive high power traction motor loads,such as is found in vehicle traction inverters. Other types of switchingdevices, including BJT (bipolar junction transistor), Insulated GateBipolar Transistors (“IGBT”), cascode amplifier and stacked transistorhigh voltage topologies, other types of FET, fluidic switching devices,MEMS devices, etc. are applicable to further embodiments. One attributeof a MOSFET is its ability to very quickly create a low resistance (Ras)conductive channel between its source and drain terminals, or to veryquickly “pinch off” that conductive channel completely to create an opencircuit (ignoring tiny amounts of current leakage) allowing the deviceto act as a low loss switch. The switching on and off of very highcurrents on very high voltage power supplies by MOSFETs 58-63 (FIG. 5)is controlled by a “gate driver” 64-69 which controls a “gate” electrodeby having a positive voltage applied to the gate electrode, V_(gs),close in magnitude to its maximum allowable voltage to switch it on, orhaving the gate electrode at approximately the same potential, withrespect to the source electrode to turn it off, respectively in the caseof an N-channel device in one embodiment. For an inverter, turning thedevice on “hard”, with a control, e.g., voltage gate to source of around15-20V in one embodiment, results in creating a minimal R_(ds)conductive channel, which means the square of current through the devicemultiplied by that R_(ds) results in minimal power loss and deviceheating. Switching the device very quickly minimizes the time thedevices spend in transition between full on and fully off states,reducing power dissipation and device heating while in the transitionregion of operation. For a typical Silicon Carbide MOSFET, a 400 ampdevice will have an R_(ds) of around 6 milliohms when the MOSFET isfully-on, resulting in a power dissipation of around 960 W. 400 amps ata HV battery voltage of 400 VDC translates to the ability to drive amotor with 160 kW of power while losing only 960 W when the switchingdevice is turned fully-on, resulting in a switching efficiency of 99.4%for the MOSFET. An EV, though, only uses about 30 kW-60 kW in normaldriving, so the thermal losses are on the order of only 34 W-70 W in theswitching device discussed in the example embodiment because losses arerelated to the square of current.

To drive a brushless motor 54, in FIG. 5, whether permanent magnet orinduction, a varying electric field needs to be created in three phases,typically, though other embodiments may have more or fewer phases. Thismagnetic field in the motor is created by varying the current in themotor's three windings 55, 56, 57, as three distinct current waveformsthat vary with time, ideally as sinusoids, and with a frequency more orless proportional to the motor rotational speed. The arrangement ofswitching devices, MOSFETS in the embodiment, is presented in FIG. 5,MOSFETs 58-63. Though the states of the switching devices for a 2-levelinverter are presented as vectors in the table 73 of FIG. 6, it isnotable that there are only 6 active states per cycle 74, where each ofthe switching transistors is fully on or fully off for a total of halfthe cycle. Fully on, by methods used by those practicing the art, meansminimal heat loss, maximum conduction, low R_(ds) by means of fullydriving the MOSFET gate with, typically, 15V to 20V. Fully off, againmeans zero current, which means 0V on the gate, but because of devicecharacteristics and leakage, SiC MOSFETS′, as in one embodiment, gatevoltages are generally driven below the potential of the MOSFET sourceterminal to negative voltages, such as −5V to fully turn the device off.

In the currently discussed embodiment of FIG. 5, each of the MOSFETs58-63 has a driver circuit 64-69, associated with its gate electrode.Upon receiving a high or low signal from a control circuit, such as anMCU, 76, the driver circuit is designed to isolate the MCU's 3-5V signalfrom the high voltages (close to the HV battery 79 voltage, such as 400VDC) at which the “high side” MOSFETS 58, 60, 62 operate on their gate(despite −5V<V_(gs)<20V), and drive the high capacitance gate withsufficient strength to quickly switch the MOSFET fully on or fully off.Switching as quickly as possible is practiced by those versed in the artto minimize the power dissipated in the region between a fully on andfully off operational state.

The embodiments add a novel element to a driver circuit by adding athird state of drive and operation to the MOSFET gate(s), which isaccording to a HEAT-signal in one embodiment. In one embodiment, thepresence of an active low HEAT-signal, devices designated as OFF intable 73, are, instead, partly turned on to where they conduct a fewamps of current. This is because the MOSFET channel is partially pinchedoff by low V_(gs) voltages of a few volts, just slightly above thethreshold turn-on voltage, “V_(th)”; in one embodiment+5V is used as anexample, where V_(th) is assumed to be around 2.5V typically. Thisvoltage will vary by device type, from device to device and even amongdevices from within the same manufacturing lot, and could be temperaturecompensated in one embodiment or self-characterized in anotherembodiment to adjust for such device variations. In one embodiment, theoperating mode of the switch device operates in a regime outside thatencountered in normal power MOSFET operational ranges for switchingapplications and it may be difficult to find characteristic devicecurves from device manufacturers, such as Ids vs. Vas for V_(gs) lessthan 10V—it's preposterous to intentionally burn power according to thethinking of many practicing the art of designing circuits utilizingswitching devices and for the switching device product definers andapplications engineers to contemplate such regions of intentionaloperation would reveal incompetence. FIG. 8 illustrates exemplarymodelling of power devices though they are not characterizations frommanufacturers and merely were rigorous validations of models againstreal semiconductor operation by the modelers.

In the embodiment where MOSFET characteristic curves 800 of FIG. 8provide a verification of the model against real device behavior, onething that seems fairly consistent is that power dissipation is readilymodulated over at least a 30:1 range using V_(gs) in the 6V to 11V areafor one example MOSFET, and related control voltages and powerdissipation are readily understood for further MOSFETs and further typesof switching devices. In one embodiment, a sense resistor or currenttransducer may be used between the source of the MOSFET and its lowerconnection (such as HV Battery negative for low side devices, or motorphase winding for high side devices) to provide feedback to finelycontrol the amount of current flowing in the partially off MOSFET. Inanother embodiment, the MOSFET is in a current mirror with a smallerdevice made in the same process. Further types of current sensors, suchas Hall Effect, induction, voltage measurement across parasiticresistance, sensing coils, etc., are readily applied to furtherembodiments. In an alternate embodiment, the objective is recognized tonot be a current level, but heating coolant to an objective temperaturewithout exceeding maximum switching device temperature ratings, so atemperature sensor in one embodiment, and a plurality of temperaturesensors in another embodiment, are used to raise or lower the powerdissipated in the switching device while in its third state ofoperation. In a further embodiment, a maximum temperature setpoint issensed resulting in switching the device from its partially on state toits fully off state, despite a command to enter the heating mode, untila lower, hysteresis temperature is obtained in order to protect theswitching device.

In one embodiment, a theoretical SiC MOSFET device has a saturated Idsdrain current of 4 amps at a V_(gs) of +5V. This means, when the matedevice in its phase leg, i.e., one of phase legs 70, 71, or 72 of FIG.5, is fully on, the HV battery's, 75, voltage (in one embodiment, 400VDC) is applied to the device, resulting in a power dissipation of400*4=1.6 kW. This power is dissipated into the MOSFET's coolingmechanism which heats a coolant in a loop. That coolant then transportsthe heat to where it will be useful, such as heating an occupant cabin,warming an energy storage device, which includes storing the heat energyitself, heating seats, or acting as a source of energy for some thermaldevice.

If the motor, 54 is not running, fully turning on the high side MOSFETS58, 60, 62 (e.g., in the driver in FIG. 5 modified to use MOSFETs inplace of IGBTs 58, 59, 60, 61, 62, 63) means no potential difference(voltage) is present across the motor windings 55, 56, 57, and thereforeno current flows in the motor. However, if the HEAT-signal is applied,the low side MOSFETs 59, 61, 63 partially turn on, each dissipates 1.6kW of heat, resulting in 4.8 kW of heat for the occupant cabin, forexample. The third state facilitates heating to occur in the switchingdevice despite the switched load having no current flowing in it, i.e.,the load is “off”. These low side devices can be modulated by PWM oneembodiment, providing a full range of thermal power from almost zero to4.8 kW, or can simply be turned on and off using “bang bang” controlmethods in another embodiment. In one embodiment, the vehicle iscoasting or stopped, using its inertia to keep moving or remainmotionless, while the motor has no current (the motor is not producingtorque) flowing in it while the low side devices are producing heat fromthe energy storage device.

The MOSFETS can also alternate their motor off duties to generateintentional heat by partially turning on both the high side and low sideMOSFETS to split the power dissipation between both devices, halving itin one embodiment, or in another embodiment by fully turning on the lowside MOSFETS 59, 61, 63 and partly turning on the high side MOSFETs 58,60, 62 (i.e., in the intermediate state), or in an alternate embodiment,PWM modulating those high side MOSFETs 58, 60, 62 with the low sideturned on. With the motor running, not fully turning OFF the deviceswhen the HEAT-signal is active, causes them to act as Joule heatingsources while the motor current is largely unaffected. In this manner,various embodiments for an electric vehicle heating system can producecombined heating, through operation of one or more of the switchingdevices in the intermediate state, and main function operation of atraction inverter, through operation of switching devices in thefully-on and fully-off state, cycling the heating mode and a mainfunction mode through each of various driver circuits. For example, anembodiment could modify Table 1 of FIG. 6, keeping the “ON” (i.e.,fully-on) states, replacing one or more of the “OFF” (i.e., fully-off)states with the intermediate state described herein, for the heatingmode of operation of the respective switching device while the inverteris operated in a main function mode to drive an electric motor. Inanother embodiment, the fully on state of the motor state table is PWMmodulated to limit motor current and the off portion of that PWM cycleenters the intermediate state described herein during the “off” portionof the PWM cycle. In various embodiments, one or more, or each of theswitching devices is operated in each of the fully-on, fully-off andintermediate states, by a respective driver circuit.

By this means, expensive resistor-based heating devices, such aselectrical PTC (Positive Temperature Coefficient resistor) air heaters,electrical PTC immersion coolant heaters and heat pumps in theembodiment where an inexpensive vehicle has no air conditioning, can becompletely eliminated for the purposes of warming occupants in thevehicle cabin, or the energy storage system, substantially decreasingthe cost of such electric vehicles that are produced in high volumes andmaking electric vehicles more accessible to lower income households.

One embodiment, shown in FIG. 9, uses the drive circuit 700 of FIG. 7 asthe basis for implementation. A theoretical device in this embodiment,as previously described herein, has characteristics of saturating at achannel current of 4 amps at a V_(gs) of +5V. The driver circuit in FIG.9 may be implemented in a number of ways, and further driver circuitswith related functionality readily devised, by those versed in the artand the embodiment in FIG. 9 is by no means the only way to implementthe embodiments, where it is desired to either use a device, or aplurality of devices, as a heat source, or as a low loss switchingdevice, based on a commanded state. In one embodiment, the HEAT-signalis used where the switching device is used as a heat source when HEAT-isactive, low, and as a high efficiency switch with low losses whenHEAT-is deactivated, high. As in FIG. 7, one embodiment of gate driverIC 77 is more or less identical, except that the source of device 81 isdisconnected from the devices in FIG. 9 and is instead connected to thedrain of device 83 in driver IC 78. Device 83's source terminal is thenconnected the way device 81 was connected in drive circuit 700 of FIG.7.

In operation, when HEAT-is inactive, high, at 87, when high efficiencyand no heating are desired, device 83 turns on and enables a path to −5Vfor any devices connected to its drain terminal. This effectivelycreates the same connections as in drive circuit 700 of FIG. 7 fordevice 81. Device 78 otherwise ignores the SIG signal which is meant toturn MOSFET 88 on and off. As such, a high on SIG will turn on device80, connecting the gate of MOSFET 88 through the R_(g_on) gate resistorto +15V provided to IC 77 by isolated power supply 89. In anotherembodiment, this voltage may be generated by use of a charge pumpcircuit. Device 81 is turned off so the gate of MOSFET 88 chargesquickly up to +15V with respect to its source 103 which is the 0Vreference of the isolated power supply 89. A low on SIG will turn offdevice 80 and turn on device 81, connecting the gate of MOSFET 88 to −5Vthrough R_(g_off), device 81, and the already on, by HEAT-being high,device 83. This fully turns off MOSFET 88 by connecting its gateterminal to −5V. The MOSFET therefore behaves identically to the MOSFETin drive circuit 700 of FIG. 7 in response to SIG and when HEAT-isinactive (high). In passing, note that the “PGND” designator of FIG. 9and the ground symbol merely designate the negative-most terminal of thecircuit block as it would appear, for example, as either the high sideor the low side switching device in a two level inverter architecture,or as for any switching device in a switching architecture.

When HEAT-is low, the embodiments cause the MOSFET 88 act as a lossydevice when off as the result of SIG being low, yet still the MOSFETturns on fully when SIG is high. When SIG is high, IC 77 functions aspreviously described by driving the gate of MOSFET 88 with +15V turningit fully on. Device 81 is off so the gate of MOSFET 88 cannot beconnected to −5V. When SIG goes low, signaling an OFF state for MOSFET88, HEAT-modifies that state to be interpreted as “slightly on”. Device80 turns off, disconnecting+15V from MOSFET 88's gate. Device 81,however, is turned on, connecting the gate of MOSFET 88 to the drain ofdevice 83. Because SIG's low signal is effectively inverted by NOR gate85, device 83 is turned off, preventing the connection from the gate ofMOSFET 88 from being completed to −5V through device 81. SIG being low,and being effectively inverted by NOR gate 85 will turn on device 82,connecting the gate of MOSFET 88 through R_(g_on) to +5V. Recall in theembodiment that when MOSFET 88's gate is at 5V, it sets up a saturatedchannel at 4 amps, no matter what voltage is applied across the MOSFET'ssource and drain terminals, MOSFET 88 is not fully turned off, as MOSFET88 was when −5V was applied as a control voltage to its gate aspractitioners in the art would do to operate MOSFET 88 in thefully-turned-off state to achieve “high efficiency” in the inverteritself, but rather MOSFET 88 is partly turned on. In one embodiment, thevoltage applied at intermediate state voltage supply 96 by supply 89 isvariable, in another embodiment, the current through MOSFET 88's drainto source path is monitored (e.g., with a current sensor 94) and thepower supply applied to intermediate state voltage supply 96 is adjustedto a regulated current value to achieve maximum safe power dissipationin MOSFET 88 to effect heating of its cooling loop. In theseembodiments, and variations thereof, the control voltage for the MOSFET88, e.g., voltage at the gate, is supplied as intermediate state voltagesupply 96 and is adjusted based on sensing current of the MOSFET 88.Alternatively, such adjustment could be made based on sensingtemperature of the MOSFET 88, for example with a temperature sensor orother sensor. The OR gate 86 is present to match propagation delays withNOR gate 85 in one embodiment. In a single isolated gate driverembodiment, the OR and NOR functions would be absorbed in a combinedlogic and control block 99, 100. Any requirement to synchronize thechanging of states of HEAT-with respect to SIG is easily implemented ifneeded by those versed in the art. A consolidated driver device, or aplurality thereof, combining the functions of 77 and 78, would haveHEAT-and SIG inputs which are isolated (functionally 97, 98) beforegoing into the logic and control blocks. Device 83 is not necessary in aconsolidated driver device and can be eliminated if the logic andcontrol block implements its effective logical AND function. Device 82would coexist in the same isolated gate driver IC as device 80, with oneconnected to the full drive supply, typically 15V to 20V, and oneconnected to a circuit that produces a control signal that creates acurrent limiting channel in MOSFET 88. Note that the partial on-state ofMOSFET 88 can be achieved by connecting to a plurality of isolatedvoltages, providing quantized steps in heat generation, or it can becontinuously variable under either open or closed loop control such asproportionality to the drain to source current, device temperature, orcoolant temperature, and can be limited, or controlled, by devicetemperature in some embodiments. Some inverters, like the one in theoriginal Model S, use a plurality of transistors as switching devices ineach phase leg, so another embodiment would simply switch one, orseveral, device(s) partially on instead of all of them if the R_(ds) ofan individual device when fully turned on is high enough or if thechannel current is sufficiently throttled within the power limitationsof the device(s). In another embodiment, a smaller, high R_(ds) device,or plurality thereof, is incorporated as part of the high power outputtransistor array, providing an inexpensive means to move thermal energyinto the coolant while adding current switching capacity. In analternate embodiment, a different R_(g_on) and R_(g_off) resistor can beswitched in, increasing the device transition time through the highpower dissipation region, increasing its power during switching of thedevice to intentionally generate heating in the switching device as acommanded switching state.

If the MOSFET 88 in FIG. 9 was connected to a 400 VDC power source byanother switching device on the opposite of the high or low side of thephase leg 70, 71 or 72, (e.g., driver in FIG. 6 modified for MOSFETs inplace of IGBTs 58, 59, 60, 61, 62, 63) to which MOSFET 88 is connected,with the embodiment's MOSFET characteristics, the +5V applied to theMOSFET 88 gate would enable 4 amps of current to flow in the device andwith a 400V applied across the device, it would dissipate 1600 W intoits cooling means. It should be appreciated that the cooling system iscapable of transferring this maximum power by such means as coolant flowrate, pump speed, heat transfer surface area, materials selection, or bydividing and conquering the problem into multiple switching devices. Inone embodiment, multiple higher R_(ds) devices are each used for the lowloss switching function and one or only a few devices are selectivelyturned on to force them to dissipate more power. By pulling HEAT-high,inactive, MOSFET 88 acts as the high efficiency, relatively low powerdissipation, switching device. With 6 devices in the three phase, twolevel, inverter configuration and with the motor in an off state, in oneembodiment three of the MOSFETs would be partially on, actingcollectively as a 3*1600 W=4800 W heat source to produce fourresidential space heaters' worth of peak, high rate passenger cabinheating, during the time the MOSFETs are in the heating state. PWMcontrol of HEAT-in one embodiment, and a variable or quantized isolatedpower supply voltage 90 in another embodiment, results in lowering ofpower dissipation as passenger cabin heating requirements level off toone or two kilowatts for a warmed cabin. The embodiments can beimplemented for an approximate added cost of $20, while also eliminatingbetween $500 and $1000 worth of an EV's resistor-based heater modules,which include heating elements, packaging, high power driverelectronics, control electronics, hoses and pipes, with typically oneset of those heater modules for occupant coolant heating and another setfor energy storage system heating. In various embodiments, the amount ofpower dissipated, and corresponding heating produced in heat mode ofoperation of a switching device is either designed for or controlled tonot exceed a power rating of the switching device, so that expectedswitch lifetime (and inverter lifetime) is preserved to levelsappropriate to expected vehicle lifetime.

FIG. 10 shows one embodiment of a claimed implementation of the of theclaimed MOSFET-heated coolant loop. In a second embodiment, the OnboardCharger (and/or the DC-DC converter implied in that block of thediagram) is placed in the loop between pump 106 and the tractioninverter 108. In one embodiment, the traction inverter 108 hasheating-mode capable MOSFETS, turned on by the HEAT-signal 109.Operation is as follows, though other implementations of the electricvehicle heating system, and the sequence of, or presence or absence ofdevices in the loop, are possible to achieve the same outcome. Thecoolant in the reservoir, “surge tank” 104, feeds a variable speedcoolant pump 106 through an opened valve 105. Valve 105 is optional andsimplistically prevents backflow of heated coolant into the surge tankor coolant loop 126. In another embodiment it can be a check valve, inanother embodiment a check valve that is closed by mild forces such assprings or magnets, and in another embodiment, it is omitted altogetherwhere gravity is exploited or flows are designed and managed. Pump 106then pushes coolant into the traction inverter 108, which contains atleast one of the claimed devices previously described that can produceheat in the presence of an activating command or signal, in thisembodiment HEAT-109.

Traction inverter 108 then passes heated coolant, in this embodiment thesystem strives for 130 degrees Fahrenheit at the inlet 123 of heatercore 118 by controlling the HEAT-signal and pump flow rate, in otherembodiments at higher temperatures such as 160° F., 170° F. or 180° F.,to heat exchanger “HEX” 111 which serves to exchange heat with theelectric motor and gearbox cooling and lubricating oil 112 in thevehicle drive unit(s). In some embodiments, multiple traction inverters108 and drive unit HEX 111 are present and multiple coolantinterconnections are possible. Suffice it to say that motor windings andgearboxes are tolerant of higher temperatures, so they are generallypreceded in the coolant loop(s) by the inverter electronics. The heatedcoolant from HEX 111 then is routed to the Onboard Charger 113, whichalso includes the vehicle's DC-DC (˜12V accessory power) module 113. Insome embodiments these are separate boxes, in one embodiment they arecombined, much as they are in the Nissan Leaf. Note that in vehicleoperation the onboard charger is turned off and only the DC-DC module isactive in most foreseeable instances. On-the-move-charging is possible(think air-to-air refueling), though, and the operation of the OnboardCharger 113 while the vehicle is in motion would simply generate moreheat in the coolant and require less heat to be produced by theheating-enabled MOSFETs (typically only in the traction inverter),assuming the heat-producing MOSFET is not implemented in the OnboardCharger (or DC-DC converter) as an embodiment, which it could be in afurther embodiment. In one embodiment, the external charging cable isliquid cooled and forms part of the Onboard Charger's heat generatingelements. In one embodiment, an external charger produces excessive heatby any means, including by the method of the invention, or has a meansof cooling, and heat is transferred to/from its coolant by means of acoolant-isolating HEX during external high speed DC charging to thevehicle's coolant to either warm the energy storage system, the occupantcabin or any combination thereof.

In one embodiment of FIG. 10, heated coolant is then routed from theonboard charger, 113, in one or more of three directions by a three-wayvalve 114. In another embodiment, a three way fitting with flowrestrictors could be used at 114. In yet another embodiment, one or moreof the three branches can have variable speed pumps to preferentiallyroute higher or lower coolant flows in their path. In yet anotherdesign, flows are engineered to produce higher and lower flows in thedifferent branched by such methods as cross-sectional areas and by useof flow restriction or enhancing devices and methods. For the purposesof heating the passenger cabin 117, heated coolant flows in line 123 tothe vehicle's heater core, which is a liquid to air heat exchanger,which is assisted in transferring thermal energy to the passenger cabinair by variable, or quantized, speed fan 119. This process transfersheat from the coolant, to the occupant cabin air, which is then returnedto junction 127 to complete the heating loop for the cabin. Any residualheat is reused in the next cycle of the loop, reducing the amount ofheat needing to be generated by the heating switching devicesincorporated into the traction inverter 108. If the cabin heating isincluded in the thermal accounting, the traction inverter becomes 100%efficient in that none of the energy from the battery is intentionallydumped overboard via the radiator 120 into the environment, unlike wouldbe the case with prior implementations of traction inverters by thoseversed in the art and where heat pumps do not harvest the “waste” heat.

Another path the heated coolant can take after exiting the OnboardCharger 113 of FIG. 10 is through the heat exchanger 115 for the energystorage system, a high voltage lithium-based battery 116 in oneembodiment. This is needed in cold ambient temperatures or for“preconditioning” the battery to reduce its internal resistance toenable faster, higher rate, battery charging or discharging in oneembodiment. For warming these batteries for greater efficiency, thetemperature only needs to be a minimum of 65F in this embodiment, thoughthis temperature could vary depending on battery technology. For fastcharging, or for higher discharge rates for high vehicle acceleration,in one embodiment, the battery is pre-heated to 130° F. to lower itsinternal resistance.

The battery HEX 115 of FIG. 10 is also fed by a second coolant loop, inone embodiment, for the purposes of either moderating the hot coolantexiting the Onboard Charger 113 and 3 way valve 114 if the cabin heateris on (in this embodiment, having a coolant inlet temperature of 130° F.at the heater core 118) to warm the battery to some intermediatetemperature (mixing hot and cold as for bathwater—lithium batteries likethe same temperatures humans do), or actually cooling the battery duringcharging or extremely hot ambient conditions. This second loop feedscoolant from surge tank 104 via branch 126 to a variable speed pump 107.The output flow of pump 107 then feeds a coolant/refrigerant heatexchanger, HEX 110, which allows an air conditioning system to cool thecoolant when it is optionally activated. If inactive, the coolant simplypasses through the HEX with its temperature relatively unchanged—thiswould be the case if the need to mix ambient temperature coolant withheated coolant arises for battery conditioning, typically when the cabinheat is on. If the cabin heat is not on, the heat from the heatedswitching devices can be modulated to turn the coolant temperature down,though some “cold” coolant mixing may still be needed. Temperaturesensors or other thermal sensors in the system are not shown in FIG. 10and their placement should be obvious to those practiced in the art andreadily understood for various embodiments in keeping with the teachingsherein. Hot and cold/cooled coolant are mixed at the inlet of thebattery HEX 115 to heat or cool the battery to desired temperatures,then the coolant is returned to the surge tank 104.

Another path the heated coolant can take after exiting the OnboardCharger 113 of FIG. 10 is via loop 122 to a radiator 120, whichexchanges heat from the coolant to ambient temperature. This loop wouldtypically be used if no cabin heating is needed and where the vehicleelectronics, such as traction inverter 108, DC-DC converter 113, ortraction motor oil 112, need cooling. Note that in one embodiment, HVbattery 116 cooling, apart from using the air conditioner HEX 110, isfacilitated by activating this loop to cool the surge tank coolant whichis also part of the battery cooling loop 126, 124, 125. The exchanger120's efficacy is assisted by the vehicle's airstream when moving(shutters 18 in front of the radiator are optional to improveaerodynamic efficiency and are not shown for simplicity) and by avariable speed fan 120. The cooled coolant then is returned to surgetank 104. In some embodiments, a heat pump is used to scavenge heatsources for heating passenger cabins and modules, like the energystorage system, so an optional placement of a heat exchanger HEX 127 canbe inserted into this coolant loop.

For systems like the Chevy Bolt EV, the embodiments described herein addone (optional) 3 way valve and eliminate: one pump, a 2 kW batteryheater 5, its controller 8, and a 7 kW cabin heater 24 (GM 42691833 MSRPis $760.49) and its controller 25; resulting in reduced: vehicle weight,complexity, leaking coolant failures, and vehicle BOM costs by severalhundred dollars per unit. In the case of the Nissan Leaf, elimination ofthe cabin heater (P/N B7413-00Q0K) MSRP, alone, is $1421.02.Approximately double the cost of the components can be realized as areduction in sticker price of the vehicle, or the savings in cost can godirectly to operating margins of the OEM, likely lifting those operatingmargins by very significant, double digit percentages.

For systems like the Tesla Model S, the embodiments described hereineliminate one pump, a battery heater and its controller 44, and a cabinheater 41. Tesla does not publish its parts prices, but those cited fromthe Chevrolet Bolt may serve as close approximations.

With reference to FIGS. 1-10, it should be appreciated that variationswith other types of switching devices, other traction invertersincluding multilevel inverters and various numbers of phases, otherdriver circuit topologies including cascode amplifiers and stackeddevices for high voltage capability, and other types of transistors andcontrolled switches, various types of sensors, various energy storagesystems, various controllers and control algorithms for operating drivercircuits and traction inverters and electric motors of various types arereadily considered and further embodiments devised therefrom. Variouspaths and components for selectively directing switching device derivedheating produced as described herein, in various vehicle systems, arereadily devised in further embodiments, in keeping with the teachingsherein.

In the event the inverter is limited in the power its switching devicescan dissipate, in one instance 1 kW per switching device in the inverterand in another embodiment a total of 3 kW of heat generation, someembodiments can also invoke the “third state” in the vehicle charger, insome embodiments while the vehicle is not even charging, which cangenerate another kilowatt of heat energy with one or more switchingdevices operating in the third state despite the charger not switchingits output devices. Further embodiments can employ other modules wherehigh power switching devices are present and liquid cooled, whetheronboard the vehicle or associated with the vehicle occasionally such asduring charging. A separate command or signal equivalent to HEAT-can beused to control each module individually in one embodiment, in anyplurality set, or collectively as one signal. The components beingdriven by the switching devices can be in their “off state” and stillhave heat generated by the switching devices that are “off”, A signalcan be implemented in either hardware or as a software state. In anotherembodiment, the contribution of each respectively is apportioned bycontrolling its percentage of the aggregate contribution of all heatsources.

Various embodiments could have an immobilizer. For example, an addedgate in the “SIG” signal path can disable a traction inverter by meansof a signal, one embodiment using an AND gate, with IMMOB—as an input.In another embodiment, the SRS (airbag) deployed signal is also used asan input to the AND gate, serving to also immobilize the vehicle in acrash. In some embodiments, the immobilization is latched logically,such that an extraordinary effort is required to reset the state of theimmobilization to enable operation again. The “signal” and the logic canalso be implemented purely in software or firmware in the inverter. TheIMMOB-signal is only inactive (high) when a state is entered where asequence such as a number, symbols, or letters, comprising a password,passcode, or security code/PIN has been correctly entered, in oneembodiment. The control circuit in the inverter may be connected toreceive this information by any communication means including CAN orother bus protocol messages, radio link such as Bluetooth or Wi-Fi, orby wired connection. Included in this is a means to enter and store theknown code in the inverter from time to time and a means to restore thatcode to a “backdoor” code to allow entry reentry or initialization ofthe code. That means could also include a restricted, code entered,access protection. Such means can be constructed by software executingon a processor, firmware, hardware or combination thereof. The enclosureand construction of the inverter is such that extensive time is required(e.g., by a hostile user) to access any means to bypass theimmobilization circuitry or software. In another embodiment, a signal isreceived from the SRS (Supplemental Restraint System, aka “airbags”)crash detection system to disable operation of the inverter until it canbe re-enabled by service technicians or the factory.

FIG. 11 depicts a method that can be practiced by embodiments describedherein. More specifically, the method can be practiced by electroniccircuitry, processors (including controllers), and various combinationsof software executing on a processor, firmware, and hardware as readilydevised in keeping with the teachings herein. The method can be embodiedin tangible, computer-readable media having instructions for executionby a processor, or plurality thereof, for example a processor in anelectric vehicle heating system as described herein.

In an action 1102, the system operates switches of a traction inverter,through driver circuits, to operate the electric motor of an electricvehicle. See, for example FIGS. 6-9 for various traction inverters anddriver circuits, and variations thereof. It should be appreciated thatthe references to operating switches of the inverter as the drivercircuits may referred to as controlling, managing, etc., the switches.In addition, the embodiments are not limited to pulling heat from thetraction inverter, as the embodiments may be extended to the chargingcircuitry for an energy storage system as discussed above.

In an action, 1104, the system operates one or more switches of thetraction inverter, or the charging circuitry of the energy storagesystem, through the respective driver circuit(s), with the switch(es) atan intermediate state in a heating mode, to produce switching deviceheating. See, for example FIGS. 6-9 for various traction inverters anddriver circuits, and variations thereof, and description of anintermediate state and heating mode and related mechanisms.

In an action 1106, the system directs switching device heating producedto heat the passenger compartment or the energy storage system of theelectric vehicle. See, for example FIG. 11, for a fluid path, selectionvalves and heat exchangers suitable for various embodiments of directingsuch switching device heating, and variations thereof. While theembodiments disclose selecting a path for the fluid or heating means itshould be appreciated that this is not meant to be limiting as the pathmay be determined through a passive manner, such as a pump being on oroff as opposed to an active manner such as valve movement. In someembodiments the heat exchanger may include ductwork supplying air flowfor cooling or warming a passenger cabin and/or energy source.

In some embodiments a method of heating a system requiring a narrowrange of temperature operation in environments requiring heat generationis provided. The method may be integrated into any power switchingapparatus, including such topologies as switching power supplies, DCmotor controls, power factor correction circuits, motor drivers,actuator controls, etc. The apparatus may be integrated into satellitesor another suitable apparatus that may utilize the heating embodimentsdescribed herein. Switching devices for the apparatus operated through adriver circuit may be utilized as described above. At least one of theplurality of switching devices of the apparatus may be operated thoughthe driver circuit with the switching device at an intermediate statebetween fully-turned-off and fully-turned-on, in a heating mode toproduce heating, as described above. The heating produced in the heatingmode is directed or controlled to heat the apparatus. The switcheddevice, or its load, does not need to be “on” for heat to be produced.It should be appreciated that in some embodiments, the device may be ina not fully on state for heat production and is not limited to a notfully off state. That is, the embodiments extend to not fully drivingthe devices so that resistive channels are heated by I²R losses vs.channel throttling V*I losses.

The foregoing description, for the purpose of explanation, has beendescribed with reference to specific embodiments. However, theillustrative discussions above are not intended to be exhaustive or tolimit the invention to the precise forms disclosed. Many modificationsand variations are possible in view of the above teachings. Theembodiments were chosen and described in order to best explain theprinciples of the embodiments and its practical applications, to therebyenable others skilled in the art to best utilize the embodiments andvarious modifications as may be suited to the particular usecontemplated. Accordingly, the present embodiments are to be consideredas illustrative and not restrictive, and the invention is not to belimited to the details given herein, but may be modified within thescope and equivalents of the appended claims.

What is claimed is:
 1. An electric vehicle (EV) heating system,comprising: a circuit to operate a switching device at a firstintermediate state, wherein the first intermediate state is betweenfully-turned-off and fully-turned-on, in a heating mode to produce heatin the switching device; the circuit to operate the switching device tohave a fully-turned-off state and a fully-turned-on state at a secondstate for a traction inverter; and the circuit operable to cycle thefirst intermediate state and the second state to provide for heating ofa cabin of the EV and for propulsion of the EV.
 2. The system of claim1, further comprising: wherein the traction inverter comprises a twolevel three-phase inverter having at least one high-side switch and atleast one low-side switch for each phase.
 3. The system of claim 1,further comprising: wherein the traction inverter comprises a multilevelinverter having a plurality of the switching device.
 4. The system ofclaim 1, further comprising: a controller to provide signals to thecircuit to operate the traction inverter.
 5. The system of claim 1,further comprising: the circuit having a current sensor; and acontroller, to sense current through the switching device via thecurrent sensor and adjust a control terminal of the switching device toadjust current of the first intermediate state.
 6. The system of claim1, further comprising: the circuit having a thermal sensor; and acontroller, to adjust a control of the circuit based on sensing via thethermal sensor.
 7. The system of claim 1, further comprising: theswitching device, with further switching devices, being disposed in thetraction inverter, each switching device operated a respective drivercircuit; and the traction inverter being disposed in a fluid path havingat least one path to a first heat exchanger for heating the cabin. 8.The system of claim 1, further comprising: the switching device, withfurther switching devices, being disposed in the traction inverter, eachswitching device operated by a respective driver circuit; and thetraction inverter being disposed in a fluid path having at least onepath to a first heat exchanger for heating an energy storage system ofthe electric vehicle.
 9. The system of claim 1, wherein the switchingdevice comprises a MOSFET (metal oxide semiconductor field-effecttransistor).
 10. The system of claim 1, wherein the switching devicecomprises an IGBT (insulated gate bipolar transistor).
 11. An electricvehicle (EV) heating system, comprising: a traction inverter having aplurality of switching devices for operating an electric motor; and acircuit coupled to one of the plurality of switching devices to: operatethe switching device at an intermediate state between fully-turned-offand fully-turned-on, in a heating mode to produce heat energy for theEV; operate the switching device to have a fully-turned-off state and afully-turned-on state in a main function mode for the traction inverter;and cycle the heating mode and the main function mode for combinedheating and main function operation of the traction inverter.
 12. Thesystem of claim 11, wherein: the traction inverter comprises athree-phase inverter having a high-side switch and a low-side switch foreach phase.
 13. The system of claim 11, wherein: the traction invertercomprises a multilevel inverter comprising multiple additional switchingdevices and.
 14. The system of claim 11, further comprising: acontroller coupled to the circuit to operate the traction inverter forboth operating the electric motor and heating one of a passengercompartment or an energy storage system.
 15. The system of claim 11,further comprising: at least one current sensor coupled to one of theplurality of switching devices; and a controller, to sense current viathe at least one current sensor and adjust a control terminal of atleast one of the plurality of switching devices to adjust current of theintermediate state.
 16. The system of claim 11, further comprising: aheat exchanger for heating a passenger compartment; and a pump to directa fluid heated in the heating mode, to the heat exchanger.
 17. Thesystem of claim 11, further comprising: a heat exchanger for heating anenergy storage system; and a pump to direct a fluid heated in theheating mode, to the heat exchanger.
 18. A method, comprising: operatingeach of a plurality of switching devices of a traction inverter througha respective circuit, to operate an electric motor; operating at leastone of the plurality of switching devices of the traction inverterthrough its respective circuit with the switching device at anintermediate state between fully-turned-off and fully-turned-on, in aheating mode to produce heating; and directing at least the heatingproduced in the heating mode to heat one of a passenger compartment oran energy storage system.
 19. The method of claim 18, furthercomprising: cycling a main function mode and the heating mode througheach of the respective driver circuits for combined main functionoperation of the traction inverter and heating function operation toheat one of the passenger compartment and the energy storage system. 20.The method of claim 18, further comprising: operating each of theplurality of switching devices of the traction inverter through therespective circuit at each of a fully-turned off state, afully-turned-on state, and the intermediate state.
 21. The method ofclaim 18, wherein the operating each of the plurality of switchingdevices of the traction inverter through the circuit to operate theelectric motor and the operating at least one of the plurality ofswitching devices of the traction inverter through the circuit heatingmode are through a controller coupled to the traction inverter.
 22. Themethod of claim 18, wherein producing the heating comprises managing apathway for traversal through one of a first heat exchanger to heat thepassenger compartment and a second heat exchanger to heat the energystorage system.
 23. The method of claim 18, further comprising: sensingcurrent or temperature of the at least one of the plurality of switchingdevices of the traction inverter; and adjusting a control of at leastone of the plurality of switching devices for the intermediate stateresponsive to the sensing.
 24. An electric vehicle (EV) heating system,comprising: a circuit to operate a switching device at a first state,wherein the first state is between fully-turned-off and fully-turned-on,in a heating mode to produce heat in the switching device; the circuitto operate the switching device to have a fully-turned-off state and afully-turned-on state at a second state for charging an energy storagesystem; and the circuit operable to cycle the first state and the secondstate to provide for heating of a cabin of the EV and for charging theEV.